Electrolytic manganese production



United States Patent Ofiice 3,034,973 Patented May 15, 1062 3,034,973 ELECTROLYTIC MANGANESE PRODUCTION James H. Jacobs, Lewiston, N.Y., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 1, 1058, Ser. No. 777,216 3 Claims. (Cl. 204-105) This invention relates to an improved electrolytic manganese process and, more particularly, to a process employing an electrolyte modifier that controls the formation of the deposited manganese metal.

In the production of metallic electrolytic manganese, the form of the deposited metal is of the greatest importance because it influences the efficiency of the process, the purity of the deposited metal, and the ease with which the deposited metal can be stripped from the cathode.

In normal operation of a manganese diaphragm compartment cell, the catholyte in the cathode compartment is maintained alkaline, even when a slightly acid feed solu tion is employed. In the normal manganese diaphragm compartment cell the feed solution is introduced into the cathode compartment. The chemistry of electrolytic manganese diaphragm compartment cells, as well as the operating practice, are described in greater detail in U.S. Patent 2,286,148 to Mantel], U.S. Patent 2,361,143 to Leute et al., and Bureau of Mines Report No. 463.

If the deposited metal is coarsely granular, it may build up on the cathode in small nodules that grow radial- 1y outward, forming a cauliflower-like structure from which the electrolyte is not easily washed. Also, in this form, the metal is not easily stripped from the cathode material when the cathode is not made of the same metal as that being deposited, since the metal tends to come off in individual nodules rather than in sheets or plates. In some processes, the deposited metal is removed from the cathodes by flexing or vibrating the latter; if the deposit is nodular, it tends to flex with the cathode and does not break loose.

Another difficulty encountered is treeing; that is, some nodules may grow at a much greater rate than the average, thus becoming much extended above the surface of the cathode deposit. In some cells, this may make it mechanically diificult to remove the cathode, or may upset current distribution (thus aggravating the condition). In addition, the nodules tend to be broken off and lost during handling, thus decreasing metal recovery.

A further difficulty encountered is the influence of cathode metal structure on the length of time the cathode can be used. Obviously, if the cathodes must be changed frequently, the overall process efficiency is greatly re duced. As mentioned above, treeing of the cathode metal, once started, becomes self-propagating and the extension of the growth of the trees can be allowed to continue only to a limited extent before the cathode must be changed, even though the volume of deposited metal is far less than physically permissible in the form of a thin, rectangular body. Therefore, the provision of any material in the electrolyte which will reduce treeing and maintain formation of a relatively flat, smooth deposit, will greatly increase the efficiency of the over-all electrowinning process.

The electrowinning of some metals is much more easily accomplished than others; copper, silver, and nickel may be electrodeposi-ted without particular difficulty. One of the metals which is more difficult to obtain electrolytically is manganese which tends to deposit in irregular fashion and in nodular form, and is very prone to form trees. For example, prior processes for electrowinning manganese were such that the deposition period was limited because of the formation of excessive projections on the metal surface. These projections not only limited the deposition period but also adversely affected the quality of the metal deposited.

Accordingly, it is the primary object of this invention to control the formation of the deposited metal and thus simplify and improve the efliciency of the process for the electrowinning of manganese by reducing the frequency at which cathodes must be removed, stripped, prepared, and reinserted in the cell.

A further object of this invention is to produce metallic manganese metal that is sound, dense, and less friable and, therefore, easier to handle and use.

Other aims and advantages of this invention will be apparent from the following description and appended claims.

The improved process by which the objects of the present invention are accomplished comprises providing and maintaining in an aqueous manganese sulphate solution during electrolysis between about 0.0015 and 0.015 part of a water-soluble polymeric acrylamide per parts of manganese in the aqueous manganese sulphate solution, whereby a thick, dense, metallic manganese deposit is produced.

It has been found that by the provision of such a concentration of a water-soluble polymeric acrylamide in an aqueous manganese sulphate solution, the character of the metal deposited at the cathode is altered from a soft to a dense, hard, compact metal. The presence of such an electrolyte modifier makes it possible to increase the continuous plating time by up to about 70 percent longer than heretofore possible. The inclusion of such a material during electrolysis has made it possible to obtain a continuous deposition of dense, hard manganese metal for periods up to about hours.

More specifically, it has been found that the provision of between about 0.0015 part and 0.015 part of a watersoluble acrylamide polymer or acrylamide-acrylimide copolymer per 100 parts of manganese in an aqueous manganese sulphate and ammonium sulphate electrolyte is eifective in controlling the formation of the deposited metal. This control of the formation of the deposited metal substantially increases the deposition period and the quality of the metal produced without any sacrifice in current efiiciency.

As is well-known in the art, a small amount of sulphur dioxide can be added to the aqueous manganese sulphate and ammonium sulphate electrolyte, in a concentration of between about 0.10 and 1.0 gram per liter, to stabilize the electrolyte and to increase current efficiency.

Addition agents suitable for use in this invention are the water-soluble polymeric acrylamide compounds. By the term water-soluble polymeric acrylamide compounds is meant acrylamide polymers and the acrylamide-acrylimide copolymers. Included among these materials are polyacrylamide and a homopolymeric acrylamide sold under the trade name of Aerofloc 30 00 by American Cyanamid Company.

A particularly effective material for the purposes of this invention is a polyacrylamide sold under the trade name of Separan 2610 by .the Dow Chemical Company. This acrylamide polymer is a polyacrylamide hydrolyte having a maximum of about 15 percent of the amide group of the polymer replaced by carboxyl groups and also having a viscosity of at least about 2 centipoises as determined at a temperature of 21.5 C. from an aqueous solution adjusted to a pH of between 3 and 5, and containing 0.5 percent by weight of the polymer hydrolyte in distilled water. This viscosity is determined using a standard OstWald viscometer.

Polymerization of the acrylamide may be carried out in accordance with the disclosure given in a technical bulletin, Chemistry of Acrylamide, published by the American Cyanamid Company, second revision, March 1956, reprinted December 1957, pages 16 and 17. Imidization may be carried out in accordance with the disclosure on page 18 of this publication. Copolyrnerization. may be carried out in accordance with the disclosure on. pages 19 through 21 of this publication.

Prior to their addition to the electrolyte in the electro-- lytic cell, the acrylamide polymers and acrylimide copoly-- mers thereof are dissolved in an appropriate solvent, such. as water, or the aqueous manganese sulphate and am-- moniurn sulphate electrolyte, and fed into the cells by any suitable method that will enable careful control of' the feed rate. The polymeric acrylamide compound se-- lected is fed into the electrolyte cell during the elec-- trolysis reaction at a rate of between about 0.001 and 0.010 gram per minute. If the additive is allowed to enter the electrolytic cell at a more rapid rate, cracking and. spelling of the deposit occurs. However, the preferred feed rate of the additive of the present invention varies for each polymeric acrylamide compound used. This preferred feed rate is determined by the surface appearance: and adherence of the deposited metal to the electrode- For example, with polyacrylamide the preferred feed rate is between about 0.006 and 0.01 gram per minute and with a homopolymeric acrylarnide such as Separan 2610, the preferred feed rate is between about 0.003 and 0.005 gram per minute.

It has also been found that when certain polymeric: acrylamide compounds are used, for example, Separan 2610, electrolytic cell cathodes having a roughened surface results in improved adherence of the metal deposits to the cathode.

In employing the improved process of the present invention, metal deposits up to about one-eighth inch thick have been obtained and the metal obtained has a bulk density of between about 7.05 and 7.21. These values were obtained by continuous depositions for periods up to about 120 hours. This represents a substantial improvement over prior processes not only in deposition time but also in the thickness, surface quality, and density of the metal deposited.

In an example of the process of the present invention, a diaphragm compartment cell containing 24 Hastelloy Alloy C cathodcs and 25 lead-silver anodes was operated under the following conditions.

Cathode current density 35 amps./ft. Temperature 35 C. Catholyte:

S 0.4 g./l.

Mn 12 g./l.

(NH SO 130 g./.

pH 8.2-8.45. Feed:

Mn 32 g./l.

pH 7.3-7.4. Rate 1.5 gal. per. min. Time of deposition 72 hours. Current efliciency 63 percent. Metal produced per day 340 pounds.

Operating under these conditions, the surface of the deposited metal was covered with nodules, some of which were loosely adhered. Also, areas of trees were present on many of the deposits. The feed solution was fed to the catholyte compartment. in the foregoing example.

A water solution of polyacrylamide containing 0.8 g./l. was then added to the catholyte compartment of the cell at a rate of 10 cc. per minute or 0.008 gram of polyacrylamide per minute. The deposited metal gradually became slightly darker and smoother. The deposition time was increased to 96 hours, the metal deposits were free of trees and the surface consisted of small, very closely packed nodules.

In another example of the process of the present invention, a cell was operated under the same conditions described in the previous example. To this cell was added a water solution of an acrylamide polymer having a viscosity of 2 centipoises. The water solution containing 0.5 g./l. was added at a rate of 10 cc. per minute or 0.005 gram per minute. The 96-hour metal, before the addition of the acrylamide polymer, was about 50 percent solid base with nodules and trees growing from the base. After the addition of the acrylamide polymer, the base on the metal was thicker and after three days, the deposits were virtually smooth with only small closepacked nodular areas.

After 120 hours deposition time, a metal deposit having a good surface was obtained.

What is claimed is:

1. In a process for the electrowinning of metallic manganese from an aqueous alkaline manganese sulphate solution in a diaphragm compartment cell, the improvement which comprises providing and maintaining dissolved in said aqueous manganese solution during electrolysis between about 0.0015 and 0.015 part of a water-soluble polymeric acrylamide per 100 parts of manganese in said electrolyte, whereby a thick, dense metallic manganese deposit is produced.

2. In a process for the electrowinning of metallic manganese employing a diaphragm compartment cell and :an electrolyte comprising an aqueous alkaline manganese sulphate and ammonium sulphate solution containing an amount of sulphur dioxide effective to stabilize the solution and increase the current efiiciency, the improvement which comprises providing and maintaining dissolved in said electrolyte solution during electrolysis between about 0.0015 and 0.015 part of a water-soluble acrylamide polymer per 100 parts of manganese in said electrolyte, whereby a thick, dense metallic manganese deposit is produced.

3. In a process for the electrowinning of metallic manganese employing a diaphragm compartment cell and an electrolyte comprising an aqueous alkaline manganese sulphate and ammonium sulphate solution containing an amount of sulphur dioxide effective to stabilize the solution and increase the current efiiciency, the improvement which comprises providing and maintaining dissolved in said electrolyte solution during electrolysis between about 0.0015 and 0.015 part of a water-soluble acrylamide polymer, having a viscosity of at least 2 centipoises, per 100 parts of manganese in said electrolyte, whereby a thick, dense metallic manganese deposit is produced.

References Cited in the file of this patent UNITED STATES PATENTS 2,497,725 Grilfith Feb. 14, 1950 2,750,338 Carosella June 12, 1956 2,798,040 Pye et al. July 2, 1957 2,810,685 Sakowski Oct. 22, 1957 2,913,377 Brown Nov. 17, 1959 OTHER REFERENCES Principles of Electroplating and Electroforming, third edition, McGraw-Hill Book Co., New York, 1949, by Boom and Hogaboom, pages 353-357. 

1. IN A PROCESS FOR THE ELECTROWINING OF METALLIC MANGANESE FROM AN AQUEOUS ALKALINE MANGANESEE SULPHATE SOLUTION IN A DIAPHRAGM COMPARTMENT CELL, THE IMPROVEMENT WHICH COMPRISES PROVIDING AND MAINTAINING DISSOLVED IN SAID AQUEOUS MANGANESE SOLUTION DURING ELECTROLYSIS BETWEEN ABOUT 0.0015 AND 0.015 PART OF A WATER-SOLUBLE POLYMERIC ACYLAMIDE PER 100 PARTS OF MANGANESE IN SAID ELECTROLYTE, WHEREBY A THICK, DENSE METALLIC MANGANESE DEPOSIT IS PRODUCED. 